Abstract Background Seasonal variations of stable hydrogen and oxygen isotopes in river water can be used to indicate hydrological processes and the water cycle in the river basin. This study presents a high-resolution time series of stable oxygen isotopic record (δ 18 O) in the lower Changjiang (Yangtze) River mainstream and aims to investigate the regional water cycle concerning natural climate changes and anthropogenic activities. Results The river water δ 18 O shows apparent seasonal variations, which is overall higher during the dry season and lower during the flood season. This basin-scale seasonal variation of δ 18 O in precipitation over the Changjiang catchment is calculated based on the long-term meteorological and hydrological data. The seasonal variation of δ 18 O in the lower Changjiang river water is largely constrained by monsoon-induced precipitation, but is more directly controlled by the mixing of waters from the upper reaches and the tributary lakes in the middle valley. Conclusions The relative contributions of waters from the upstream and tributary lakes to the lower Changjiang mainstream have been considerably altered by the construction of Three Gorges Dam via the regulation of river discharges. A comparison of river water isotopic records with water discharges from the lakes suggests that it takes about 2 weeks (~ 17 days) for the Changjiang river water to circumvent the mid-lower reaches of the catchment before traveling to the sea. This study suggests that the stable hydrogen and oxygen isotopes can be harnessed as sensitive indicators for water cycling within a large catchment that is driven primarily by natural forcing though subject to substantial human impacts.
Rare earth elements (REEs) are powerful tools to track oceanic biogeochemical processes.However, our understanding of REE sources is incomplete, leading to controversial interpretations regarding their oceanic cycling.Continental margin sediments are often assumed to be a major source, but the sediment pore water data required to understand the processes controlling that potential source are scarce.Here, we measure and compile pore water and estuarine REE data from the Changjiang (Yangtze) estuary-East China Sea shelf.We show that release of REEs, from shallow pore water to overlying seawater, is coupled to Mn reduction.In contrast, REEs are removed in deep pore water, perhaps via formation of an authigenic REE-bearing phase.This sedimentary source can potentially explain REE addition in the estuary at mid-high salinity.Our calculations suggest that the benthic flux is the largest Nd source (∼40 %) on the East China Sea shelf.Globally, however, despite a higher benthic Nd flux on the advection-dominated shelf, the much more extensive deep ocean still dominates the total area-integrated benthic flux.Our results call for a more extensive investigation of the magnitude of the benthic flux of REEs to the oceans.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
